xgrabsc is an X-windows screen dumping utility. It is much more
flexible than most such tools, allowing one to grab arbitrary screen
portions and windows, and dumping them in a large number of output
formats, including several Postscript formats, x-bitmap, and
portable-bitmap.

xgrabsc is available via anonymous FTP from ftp.x.org in the 
directory /contrib/applications/.

xgrabsc is not a GNU program.